Dialkylzinc has been conventionally often used as a catalyst or a reaction agent for polymerization or production of pharmaceuticals, or as a substance for forming zinc oxide that forms a transparent conducting film used for electrodes of solar cells or semiconductor devices.
As one of the methods for manufacturing dialkylzinc, a reaction of zinc chloride and trialkylaluminum shown in the equation (1) has been known as described in Patent Documents 1 and 2.ZnCl2+2R3Al→R2Zn+2R2AlCl  (1)
In this method, trialkylaluminum (R3Al) as a raw material is a product obtained by reacting aluminum, hydrogen, and an alkene in the presence of trialkylaluminum. The product, however, contains hydrides such as R2AlH, RAlH2, and AlH3 as impurities. As pointed out in Non-Patent Document 1, when trialkylaluminum having a high concentration of a hydride is used as a raw material for the reaction with zinc chloride, a metallic zinc or the like deposit along with the reaction proceed. Further, precipitates deposit during the distillation of dialkylzinc after the reaction. Therefore the precipitates adhere to an inner wall of an apparatus so that the reaction or distillation is forcibly interrupted. In addition to this, there are other problems that it takes a long time to wash the apparatus, and that a heat conduction effect of a heater is reduced.
Here, it is recognized that dialkylaluminum monochloride obtained as a by-product in the reaction of zinc chloride with trialkylaluminum has a catalytic activity for various polymerization reactions, and the demand thereof is increasing.
Dialkylaluminum monochloride is contained in a still residue after dialkylzinc having high volatility is distilled from the reactant solution of the above-mentioned reaction, and can be obtained from this still residue. As mentioned above, however, a large amount of the precipitates such as metallic zinc is contained in the still residue after dialkylzinc is distilled from the reactant solution of the above-mentioned reaction of zinc chloride and trialkylaluminum. Zinc is contained in dialkylaluminum monochloride obtained by distilling this still residue. In addition, similarly to the case of distillation of dialkylzinc, it is difficult to continuously perform distillation separation due to a large amount of precipitates.
Various methods for reducing a concentration of zinc in dialkylaluminum monochloride are reported. Examples thereof include a method for adding trialkylaluminum containing alkylaluminum hydride to a still residue after dialkylzinc is distilled, which is described in Patent Document 3; and a method for adding alkylaluminum sesquichloride to a still residue after dialkylzinc is distilled, which is described in Patent Document 4. However, the boiling point of dialkylaluminum monochloride approximates that of trialkylaluminum or alkylaluminum sesquichloride that have alkyl groups with the same number of carbon atoms, and separation thereof by distillation is difficult.
Furthermore, Patent Document 7 reports a method for heating a still residue at 150 to 240° C. in an inert gas atmosphere after distillation separation of diethylzinc, and Patent Document 8 reports a method for adding aluminum chloride and triethylaluminum to be heated, and subsequently distilling dialkylaluminum monochloride. However, these methods increase the steps. In addition, the concentration of zinc in dialkyl aluminum monochloride obtained is 200 mass ppm or 100 mass ppm or the like, and not sufficiently reduced.
Patent Documents 5 and 6 report use of silicon oxide, water, or the like as an additive as a method for suppressing deposition of metallic zinc in the reaction of zinc chloride with trialkylaluminum. However, it cannot be said that the effect is sufficient, and it is accompanied by a sacrifice of reduction in productive efficiency of dialkylzinc.
In order to obtain trialkylaluminum having a low concentration of a hydride that leads to deposition of metallic zinc, it may be thought that the partial pressure of the alkene as the raw material is increased upon synthesizing trialkylaluminum. However, when the partial pressure of the alkene is increased during synthesizing trialkylaluminum, the alkenes react with the alkyl groups to produce trialkylaluminum having polymeric alkyl groups. By using the produced trialkylaluminum having one or more polymeric alkyl groups as a raw material, dialkylzinc having one or two polymeric alkyl groups is contained in the reactants of the reaction of zinc chloride and trialkylaluminum. The dialkylzinc having one or two polymeric alkyl groups has a boiling point higher than that of dialkylzinc having monomeric alkyl groups, and has a boiling point close to that of dialkylaluminum monochloride. Accordingly, the dialkylzinc having one or two polymeric alkyl groups is mixed with the dialkylaluminum monochloride obtained by distillation separation. For this reason, even if trialkylaluminum which is obtained by increasing the partial pressure of the alkene during synthesizing is used as a row material, a yield of dialkylzinc is reduced and separation of dialkylaluminum monochloride with high purity is difficult.
As mentioned above, in manufacture of dialkylzinc and dialkylaluminum monochloride using zinc chloride and trialkylaluminum as raw materials, a method is demanded in which production of precipitates in the reaction process, and adhesion of precipitates to equipments are suppressed and productivity is not decreased, and both of dialkylzinc and dialkylaluminum monochloride are produced with high purity and yield and on a satisfying industrial scale.
Prior Documents
Patent Documents
    [Patent Document 1] JP37-2026B    [Patent Document 2] U.S. Pat. No. 3,124,604    [Patent Document 3] U.S. Pat. No. 4,732,992    [Patent Document 4] U.S. Pat. No. 4,670,571    [Patent Document 5] JP2863321B    [Patent Document 6] JP2863323B    [Patent Document 7] U.S. Pat. No. 3,946,058    [Patent Document 8] U.S. Pat. No. 4,092,342Non Patent Literature    [Non Patent Document 1] J. Am. Chem. Soc., 73, 4585, 1951